The present invention relates to a permanent magnet and in particular to a permanent magnet rotor for an electric machine.
The invention also relates to a method for manufacturing such a permanent magnet.
In a preferred embodiment the permanent magnet according to the invention is a permanent magnet rotor for a machine.
Many different types of permanent magnetic materials to be used in rotors are available on the market. Which material to select often depends on a balancing between the desired magnetic strength of the rotor and the price of the materials for the rotor, e.g. the magnetic powder. Furthermore, many other parameters, such as corrosion, temperature, the work-point of the magnet, etc., will influence the choice of selection.
Available permanent magnetic materials comprise ferrites and NdFeB, SmCo or AlNiCo. Magnets made of these materials can be manufactured in many ways, but the most selected ways are sintering, injection molding or bonding.
Sintered magnets are made by compressing the magnetic powder under high pressure, followed by sintering in a suitable furnace.
Bonded magnets are made of a composite of a magnetic powder comprising a binder. The permanent magnet is formed by compressing the composite in a mold. European patent application publication EP 1 722 457 A2 discloses a motor with a rotor comprising a bonded magnet of this type.
Disadvantages of using the mentioned magnets in rotors are that sintered magnets are generally relatively expensive to manufacture due to a complicated manufacturing process, and bonded magnets are generally not as efficient as sintered, e.g. due to their content of non-magnetic binder material.